The present invention relates to an optical connector ferrule serving as a component of an optical connector and used for connection of a fiber optic ribbon cable, a mold for molding a ferrule, a method of manufacturing an optical connector ferrule, and a method of inspecting an optical connector ferrule.
FIGS. 18 and 19 show a pair of optical connectors Cg called MT connectors. Each optical connector Cg has an optical connector ferrule 81B and fiber optic ribbon cable 82. The ferrule 81B is made of a molding resin and mounted on an end of the fiber optic ribbon cable 82. The ferrule 81B has a pair of guide holes 92 and fiber positioning holes 93. The openings of the pair of guide holes 92 and fiber positioning holes 93 appear on an end face 91 opposing the optical connector Cg to be connected. The respective optical fibers, contained in the fiber optic ribbon cable 82, are arranged in the fiber positioning hole 93. The pair of guide holes 92 extend through the ferrule 81B from the one end face 91 to the other end face opposing the one end face. A stainless guide pin 83 is inserted into each of the pair of holes 92. As shown in FIG. 19, the guide pins are inserted into the guide holes 92 and positioned therein, whereby the pair of optical connectors Cg are connected to each other. This connection is held using a clamp spring 85. JIS C5981 provides detailed description of this optical connector type.
The present inventor found the following problems in the course of studying these optical connectors.
Each optical connector Cg has the guide pins 83 and resin ferrule 81B. Since the thermal expansion coefficient of the guide pins 83 is different from that of the ferrule 81B, temperature change causes stresses between the guide pins 83 and guide holes 92. Owing to these stresses, the positions of the optical fibers held in one optical connector Cg may shift from the positions of the optical fibers held in the other optical connector Cg. The inventor thinks that such shifts increase connection loss between these connectors.
Japanese Patent Laid-Open No. 6-138344 discloses a technique associated with an optical connector. This optical connector includes two different types of guide members in a resin ferrule. One of these types of guide member includes fiber fixing grooves for fixing optical fibers and guide projections. The other of these types of guide members includes fiber fixing grooves for fixing optical fibers and guiding depressions. Each of guide members is integrally formed with an Invar alloy. Each fiber fixing groove has a rectangular cross-section with a bottom and two sides. Each guide projection has a rectangular cross-section. The guiding depressions guide the guide projections inserted thereto with the two opposite sides of the guiding depressions.
The inventor paid attention to the following point in the course of studying the optical connector disclosed in the above reference.
Since each fiber fixing groove has a bottom surface and two sides, the fixed optical fiber is surrounded by three surfaces of the Invar alloy and one surface made of material different from Invar Alloy. The guiding depressions guide the inserted guide projections by the two opposing side surfaces thereof. For this reason, each guide projection is surrounded by the two surfaces made of one material and the two surfaces made of another material. The optical fibers, guide projections, and guiding depression is accommodated in the connector are surrounded in a plurality of kinds of materials. With temperature changes, various thermal stresses, dependent on the materials they contact, are applied to these accommodated components. The inventor thinks that the thermal stresses may interfere with higher-speed transmission.
It is, therefore, an object of the present invention to provide an optical connector ferrule that allows the formation of an optical connector having good transmission performance, a mold available for the formation of the ferrule, a method of manufacturing the ferrule, and a method of inspecting the ferrule.
An optical connector ferrule according to the present invention comprises one or more optical fiber accommodating holes, a mating surface, a first guide projection, and a guide engaging portion. Each of the optical fiber accommodating holes has an inner surface and one end portion. The inner surface is made of resin and extends along a predetermined axis. The inner surface are provided so as to face the side surface of the optical fiber when an optical fiber is inserted into one of the optical fiber accommodating holes. The openings of the optical fiber accommodating holes appear in the mating surface. The first guide projection and guide engaging portion continuously extend from the mating surface along the predetermined axis so as to be allowed to position the connector with another connector to be connected. The optical fiber accommodating holes, mating surface, first guide projection, and guide engaging portion are made of one piece molded resin.
Since the optical fiber accommodating holes, first guide projection, and guide engaging portion are formed into an integral component with resin, there is no need to use any positioning components made of different materials, e.g., metal guide pins. Since no additional positioning components are required, stresses due to temperature changes do not concentrate on any specific part of the ferrule. In addition, since the stresses are dispersed throughout the ferrule through the integral resin, deformation due to such stresses does not occur in only specific part of the ferrule. This reduces the positional offsets of the optical fiber accommodating holes due to temperature changes. This improves the positioning precision between the ferrules of a pair of connectors to be connected to each other.
In the ferrule according to the present invention, each optical fiber accommodating hole can be formed between the first guide projection and guide engaging portion. This facilitates inspecting the positions of the optical fiber accommodating holes. In addition, since the guide projection and guide engaging portion are disposed so as to sandwich the optical fiber accommodating holes, this can compensate on positional offset due to the deformation of the guide projection and guide engaging portion. The guide engaging portion may be a second guide projection or guide hole.
In the ferrule according to the present invention, the guide engaging portion can include a second guide projection, made of resin, continuously extending from the mating surface along the predetermined axis. Both the first and second guide projections, made of the same material, continuously extend from the mating surface along the predetermined axis. This further improves the positioning precision of optical fiber accommodating holes which is affected by temperature changes.
In the ferrule according to the present invention, each of the first and second guide projections has a cross-sectional area of the proximal portion gradually increasing toward the mating surface along the predetermined axis. As the cross-sectional area increases, the mechanical strength is enhanced in the proximal portion of each guide projection on which forces tend to concentrate in the attachment/detachment of the ferrule.
In the ferrule according to the present invention, each of the first and second guide projections has a circular cross-section taken on a plane intersecting the predetermined axis. The high symmetry of the cross-sectional shape is advantageous to keep the linearity of the projection even when the guide projection is made of resin. This further improves the positioning precision of the optical fiber accommodating holes.
In the ferrule according to the present invention, the guide engaging portion can include a guide hole with an inner surface made of resin extending along the predetermined axis, and a bottom surface made of resin.
Since the ferrule has a guide projection and guide hole that extend along the predetermined axis, these ferrules can be applied to a pair of connectors to be connected to each other. That is, the guide projection of one ferrule is inserted into the guide hole of the other ferrule. Since the guide projection is inserted into the guide hole made of the same material, temperature change deforms the guide projection and guide hole in the same manner. This improves the positioning precision of the optical fiber accommodating holes.
In the ferrule according to the present invention, the first guide projection has a cross-sectional area, in the proximal portion, gradually increasing toward the mating surface along the predetermined axis. In addition, in the ferrule according to the present invention, the first guide projection has a circular cross-section defined on a plane intersecting the predetermined axis.
In the ferrule according to the present invention, the inner surface of the guide hole can include a first tapered surface, which extends along the predetermined axis and tilts with respect to the side surface thereof, around the opening portion of the guide projection. The first tapered surface allows the guide projection to be smoothly inserted into the guide hole.
In the ferrule according to the present invention, the guide hole has a circular cross-section on a plane intersecting the predetermined axis. Since the guide hole has the high geometrical symmetry of the cross-section, high positioning precision can be maintained even if the guide hole thermally expands or shrink.
In the ferrule according to the present invention, the first guide projection has a second tapered surface, which tilts with respect to the predetermined axis, on the distal end portion. This facilitates the positioning of the guide projection to the guide hole into which the guide projection is inserted.
In the ferrule according to the present invention, the inner surface of the guide hole can include a third tapered surface, which extends along the predetermined axis and tilts with respect to the inner surface, around the opening portion thereof. The first guide projection can include a fourth tapered surface, which tilts with respect to the predetermined axis, on the distal end portion thereof. The third tapered surface is tilted in an angle associated with that of the fourth tapered surface.
The fourth tapered surface can increase the mechanical strength of the proximal end portion of the guide projection. The third tapered surface ensures that the guide hole accommodates the reinforced guide projection. Since the fourth tapered surface of the guide projection is made of the same material as the third tapered surface of the guide hole receiving the guide projection, the guide projection and guide hole deform similarly near the mating surface due to thermal expansion/shrinkage. This behavior improves the positioning precision of each optical fiber accommodating hole.
The ferrule can be molded using injection molding. This method shortens the molding cycle time and hence can improve productivity.
In the ferrule according to the present invention, the resin material for integrally forming this ferrule preferably includes a PPS resin containing 39 to 65 wt % of silica particle filler and 26 to 35 wt % of silicate whisker filler, with the total content of the silica particle filler and silicate whisker filler being 65 to 85 wt %.
The use of this resin allows higher dimensional accuracy and mechanical strength of molded products and can decrease the dimensional variations of the molded products with time. When a thermoplastic resin is used, a good releasability from a mold is provided, and damage to the guide projection may sustain can be suppressed in a releasing process.
A mold for molding the ferrule according to the present invention comprises first, second, third, and fourth mold units for defining a cavity for forming the ferrule. When the first unit is positioned to the second mold unit so as to define the cavity, a housing portion is provided. In the housing portion, the third and fourth mold units are accommodated. The third and fourth mold units are moved along the predetermined axis so as to be housed in the housing portion. The third and fourth mold units can be moved relative to the combined first and second mold units.
In the mold for molding the ferrule according to the present invention, the third mold unit has a guide projection forming portion, at least one pin, and an engaging portion forming portion. The guide projection forming portion has an inner surface extending along the predetermined axis and a bottom surface so as to form a guide projection of the ferrule. The pin extends along the predetermined axis so as to forming a fiber accommodating portion of the ferrule. The engaging portion forming portion extends along the predetermined axis so as to form an engaging portion of the ferrule. The pin of the third mold unit has a distal end portion on which a tapered portion is formed.
In the mold for molding the ferrule according to the present invention, the third mold unit has a pair of guide projection forming portions and one or more of pins. These pins can be arranged between the pair of guide projection forming portions.
In the mold for molding the ferrule according to the present invention, the third mold unit has a guide projection forming portion, a projection, and one or more of pins. The projection has a side surface extending along the predetermined axis to provide a guide hole of the ferrule. These pins can be arranged between the guide projection forming portion and the projection.
Since this mold comprises the first, second, third, and fourth mold units for defining the cavity for forming a ferrule, the ferrule can be integrally molded with the resin. Therefore, the optical connector ferrule having the advantages above can be easily and reliably manufactured.
The third and fourth mold units can be moved relative to the first and second mold units along the predetermined axis. This allows the manufacturing of a ferrule having a guide engaging portion, guide projection, and guide hole which can be accurately positioned to a ferrule accommodating hole.
In the mold for molding the ferrule according to the present invention, the third mold unit has a vent extending from at least one of the bottom and inner surfaces of the guide projection forming portion to the surface of the third mold unit. This vent serves as a gas releasing hole when a molten resin flows into the guide projection forming portion, and hence allows the resin to easily flow into the guide projection forming portion. Since the resin flows toward the bottom surface, the vent is preferably formed in the bottom surface. To effectively release a gas while preventing leakage of the resin flow, the diameter of the vent is preferably set to 0.1 mm or more and 0.2 mm or less.
The inner surface and bottom portion of the guide projection forming portion can be coated with chromium nitride. This chromium nitride coating improves the releasability for the projection forming portion when the molded ferrule is released, and hence is effective in suppressing damage to the guide projection in the releasing process. Even if the guide projection is free from damage, the coating is useful in keeping the high dimensional accuracy of the guide projection. This allows the manufacturing of the ferrules that realize good transmission characteristics.
A method of suitably manufacturing the optical connector ferrule according to the present invention comprises the following steps: (1) preparing a mold disclosed in the specification; (2) providing a molding resin into a mold to form a ferrule; and (3) inspecting the positions of fiber accommodating holes of the ferrule with respect to guide projections or guide holes thereof, and separating a resin molded product that has passed the inspection and a resin molded product that have failed to pass the inspection.
The following inspection method can be applied to the method of manufacturing a ferrule.
The method of inspecting the optical connector ferrule according to the present invention allows the inspection of the positions of the fiber accommodating holes with respect to those of the guide projections in the ferrule.
This method comprises the following steps: (4) preparing a jig having a pair of positioning holes, the positioning holes extending through the jig from a first surface to a second surface, first and second guide projections are inserted into the pair of positioning holes; (5) receiving light passing through the pair of positioning hole of the jig to determine the positions of positioning holes on the basis of the received light; (6) inserting the first and second guide projections into the positioning holes; (7) receiving light passing through fiber accommodating holes to determine the positions of the fiber accommodating holes on the basis of the received light; and (8) inspecting the positions of the fiber accommodating holes with resect to the pair of guide projections on the basis of the determined positions of the positioning hole and the fiber accommodating holes.
A method of inspecting an optical connector ferrule according to the present invention comprises the following steps: (9) preparing a first jig having a pair of positioning holes provided so as to insert first guide projections therein and extending through the jig from a first surface thereof to a second surface thereof; (10) receiving light passing through the pair of positioning holes of the first jig to determine the positions of the positioning holes of the first jig; (11) preparing a second jig having a positioning projection provided so as to be inserted into the first guide hole, and inserting the positioning projection of the second jig into one of the pair of positioning holes; (12) inserting the guide projection of the ferrule into the other positioning hole, and inserting the positioning projection into the guide hole of the ferrule; (13) receiving light passing through fiber accommodating holes to determine the positions of the fiber accommodating holes on the basis of the received light; and (14) inspecting the positions of the fiber accommodating holes with respect to those of the pair of guide projections in accordance with the determined positions of the positioning hole and the fiber accommodating holes.
A jig having positioning holes positioned to guide projections is prepared. The positions of the positioning hole and the optical fiber accommodating holes are optically measured. The position data for one of the positioning hole and fiber accommodating holes is used as a reference to determine the other position. With this operation, in the ferrule of an integral resin body including guide projections and guide holes, the positions of the fiber accommodating holes with respect to the guide projections and guide holes can be accurately inspected.